The invention concerns a safety insert for storage vessels of low-boiling, liquified gases.
In storage vessels for low-boiling gases which have a necklike opening for filling and extraction, helium tanks for, example, there is a danger, as a result of air penetration, that water vapor, carbon dioxide or air will freeze out in the vessel neck and clog the neck. Since the low-boiling, liquified gas vaporizes further in the vessel, great pressure builds up in the vessel which finally destroys the vessel through an explosion.
Safety inserts are used to preclude this danger. Such a safety insert consists of a safety neck tube placed in the neck of the vessel, which forms an annular space with the vessel neck. The safety neck tube is sealed from the exterior and has take-up devices for a siphon for the filling and extraction of the liquified gas, as well as connections for a safety valve and optional additional apparatuses. The vent pipe for extracting the liquified gas is mounted onto the vessel neck. This vent pipe represents a junction of the annular space in the vessel neck with the exterior. During normal operation, the vaporized gas flows outward through this pipe. When excess pressure builds up in the neck, for example, as a result of non-extraction of vaporized gas over a longer period of time, vaporized gas flows away through the safety neck tube and the safety valve. During normal operation, therefore, there is a gas column in the safety neck tube and a flowing gas quantity in the annular space. The latter is very desirable for an intense, so-called neck gas cooling. For this reason, the annular space is made narrow to maintain as great a flow velocity as possible.
The gas column in the safety neck tube is disadvantageous, however. Namely, a noticeable heat transfer to the liquid by gas-heat conduction results through the stationary gas column.